package jdbc;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class JDBCDemo5 {
    public static void main(String[] args) {
        try (
                Connection connection = DBUtil.getConnection();
        ) {
            Statement statement = connection.createStatement();
           /*
           SELECT COUNT(*) count
           FROM class c
           JOIN student s ON s.class_id=c.id
           WHERE c.name='1年级1班'
            */
            String sql = "SELECT COUNT(*) count\n" +
                         "FROM class c\n" +
                         "JOIN student s ON s.class_id=c.id\n" +
                         "WHERE c.name='1年级1班'";
            ResultSet rs=statement.executeQuery(sql);
            if (rs.next()){//因为统计的结果只有一条记录，所以无需用while
                int count=rs.getInt("count");
                System.out.println("共"+count+"人");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}
